Three of the four guests who attended a family lunch in a quiet Australian country town died shortly afterward, with symptoms the police said were consistent with mushroom poisoning. The fourth spent nearly two months hospitalized, critically ill.

The case has gripped the nation and led to intense speculation. The woman who cooked the meal has always strongly maintained her innocence. On Thursday, three months after the lunch in question, police charged her on counts of murder and attempted murder.

Erin Patterson, 49, hosted the lunch on July 29, at her home in Leongatha in the state of Victoria. In attendance were Gail and Don Patterson, the parents of her estranged husband, as well as Gail Patterson’s sister, Heather Wilkinson, and brother-in-law, Ian Wilkinson.

All four guests, who were in their 60s or 70s, fell ill soon after the meal. Mr. Patterson, Ms. Patterson and Ms. Wilkinson all died within a week of the lunch. Mr. Wilkinson eventually recovered and was released from the hospital in late September.

Their symptoms, the police said at the time, were consistent with poisoning by death cap mushroom — one of the deadliest mushroom varieties, which is found in Victoria and other parts of Australia.

Ms. Patterson has consistently denied wrongdoing. She tearfully told local news media in August that she “didn’t do anything, I loved them.”

She was taken into custody on Thursday morning, according to Victoria Police, and her house was searched by dogs trained to hunt down items like USB sticks and SIM cards.

A few hours later, she was charged with three counts of murder and five counts of attempted murder. The attempted murder charges included three prior, separate episodes, in all of which a 48-year-old man got sick, the police said in a statement.

“I know that people will no doubt have many unanswered questions about this matter, however I urge people to be especially mindful of unnecessary speculation and not sharing misinformation,” Detective Inspector Dean Thomas said.

He also acknowledged the attention the case has received: “Over the last three months, this investigation has been subjected to incredibly intense levels of public scrutiny and curiosity. I cannot think of another investigation that has generated this level of media and public interest, not only here in Victoria but also nationally and internationally.”

Ms. Patterson is scheduled to appear in court on Friday morning.

In a statement provided to the police in August, which was obtained by local news media outlets, Ms. Patterson said that she had prepared a meal of beef Wellington that day, using fresh mushrooms bought from a local supermarket and dried mushrooms bought from an Asian grocer in Melbourne, which is about 85 miles northwest of Leongatha.

She said that she also ate the beef Wellington that day. The next day, her two children ate the leftovers for lunch, she said, but added that she scraped off the mushrooms from their portions because they do not like them.

Ms. Patterson said that she had also been hospitalized after the lunch with bad stomach pains and diarrhea but was given a “liver protectant drug.”

In her statement, Ms. Patterson said that she had discarded a food dehydrator at a dump.